Two Methods of Getting an Image from URL: The Differences? - objective-c

Question

What are the main differences between the following two methods of fetching a UIImage from a URL? I recently switched from Method 1 to Method 2 in my app and seemed to experience a drastic increase in speed when I thought that, essentially, both methods were nearly the same in practice. Just trying to figure out why I saw such a speed increase.
Method 1
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *imageData = [NSData dataWithContentsOfURL:self.imageURL];
dispatch_async(dispatch_get_main_queue(), ^{
self.image = [UIImage imageWithData:imageData];
});
});
Method 2
- (void)fetchImage
{
NSURLRequest *request = [NSURLRequest requestWithURL:self.imageURL];
self.imageData = [[NSMutableData alloc] init];
self.imageURLConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
if(connection == self.imageURLConnection)
{
[self.imageData appendData:data];
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
if(connection == self.imageURLConnection)
{
self.image = [UIImage imageWithData:self.imageData];
}
}

Answer 1

My best guess is that because for Method 1 the AsyncURLConnection class multithreads:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
/* process downloaded data in Concurrent Queue */
dispatch_async(dispatch_get_main_queue(), ^{
/* update UI on Main Thread */
So, you may see degraded performance due to contention for shared resources.
On the other hand Method 2, is actually just a collection of methods which are implemented more like transaction processing.
There's probably also more to it.